Coated radiation emitting bulb



Dec. 21, 1943. e. H. MERIDITH 2,337,485

COATED RADIATION EMITTING BULB Filed Mar ch. 1, 1943 His A't'for'neg.

Pmma Dec. 21,1943

COATED RADIATION EMITTING BULB George H. Meridith, Cleveland, Ohio, assignor to General Electric Company, a corporation of New York Application March 1, 1194s, Serial No. 477,671

9 Claims. ((31. 67-31) My invention relates, in generaL- to electric lamps and similar devices for the production of invisible radiations, such as infrared or ultraviolet radiations, and to the manufacture of such devices. More particularly, my invention relates to means for rendering the glass envelope or bulb of such devices impervious to visible radiations while permitting the transmission therethrough of invisible radiations such as infrared or ultraviolet rays. I

It has been known heretofore to coat the glass bulbs of photoflash lamps, such as are used for photographic purposes, with a. layer of an infrared or ultraviolet transmitting lacquer capable of absorbing and blocking out any and all visible radiations generated within thebulb. Such flash lamps are especially suitable for so-called blackout photography. The usual procedure, in applying such a lacquer coating to the bulb, is to simply immersethe lamp bulb in a bath of the.

lacquer material and to then introduce the coated lamps into an'oven or drying chamber where the lamps are heated to dry the lacquer coating on the bulbs. With such procedure, however,it has been found that for some reason or other, numerous air or gas bubbles are formed in the lacquer coating immediately adjacent the junction between the lamp base and bulb. It may be that such bubbles result from the presence of trapped air within the annular space between the base shell and the bulb. Such a bubble formation permlts the passage of visible radiations therethrough so that the lamp is not completely lighttight. Moreover, on drying, the lacquer coating bridging the gap between the lamp bulb and the rim of the base shell stretches thin to such a degree as to permit the transmission of visible radiations therethrough.

It is an object of the present invention to overcome the above-mentioned defects and provide a lamp the bulb of which is positively light-tight.

Another object of my invention is to provide a photofiash lamp which will emit a flash of actinic radiation solely within the infrared region of.

the spectrum.

Further objects and advantages of my invention will appear from the following description of a species thereof and from the accompanying drawing, in which:

Fig. 1 is an elevation, partly in section, of a lamp comprising my invention; Fig. 2 is a fragmentary section, on an enlarged scale, of the base and the adjacent neck portion of the bulb of the lamp shown in Fig. 1; Fig.3 is a fragmentary view, partly in elevation and partly in section,

of the lamp shown in Fig. 1 at an intermediate stage in its manufacture, the section being taken at the side soldered connection; and Fig. 4 is a. view, similar to Fig. 2, showing the lamp comprising my invention at a later stage in its manufacture.

Referring to the drawing, the'invention is there shown in connection with a photoflash lamp of a well-known type used for photographic pur-' poses. The lamp comprises a glass bulb l0 having a neck portion H to which a base I2 is attached by a ring or layer of basing cement l3 (Fig.2). The said base comprises a metal shell portion l4 provided at one end thereof with a bottom or center contact eyelet I5 fastened to the shell N. by a button l6 of insulating material, such as glass. The other or open end of the base shell Id surrounds the neck H of the bulb Ill and is secured thereto by the basing cement 13 which is disposed in the annular space between the bulb neck and the surrounding portion of the base shell. The basing cement I 3 may comprise a mixture of a synthetic resin such as Bakelite,

rosin, a filler such as marble flour, a agent such as shellac, and alcohol.

The bulb i0 is provided with a re-entrant stem ll extending inwardly from the neckend of the bulb and having a pair of leadingr-in wires l8, l9 sealed therein and extending therethrough. The outer ends of the said leading-in wires I8, 13 are connected to the metal shell l4 and the bottom contact eyelet l5, respectively, of the lamp base l2, the wire I8 being bent back over the rim 20 binding of the base shell, through a notch 26 (Fig. 3) in the said rim, and soldered to the exterior surface of the shellwhile the other wire I9 extends through the eyelet l5 and is soldered thereto. Most of the bubbles referred to hereinabove form in the lacquer bulb coating adjacent the soldered connection at the notch 26.

Disposed within the bulb I0 is an ignition filament 2| which is connected to and supported by the inner portions of the leading-in wires l8, l9. The inner ends of the said leading-in wires and the adjacent portions of the filament 2| are coated with a layer of a suitable fulminating substance or primer 22.

The bulb It] may be filled with a quantity of readily combustible flash material 23 loosely arranged in the bulb within effective ignition range The combustible material 23. may consist of the wellknown leaf foil, wire or shredded foil of aluminum ,and/or magnesium, or alloys thereof. The bulb it) also contains a filling of oxygen or oxygencontaining gas at a suitable pressure for supporting the combustion of the combustible material 23. The pressure of this gaseous filling will vary between about 180 and 600 mm., depending upon the type of gas employed, the size of the bulb, and the quantity and type of combustible material therein.

When an electric current is passed through the filament 2|, the heating of the filament by such current immediately ignites the primer 22 which in turn ignites the combustible material 23. The ensuing combustlonwof the combustible material 23 then produces a flash of actinic light of relatively high intensity. The light so generated is composed of radiations within both the visible and invisible (infrared and ultraviolet) regions of the spectrum.

In accordance with the invention, the bulb in is provided with a filter in the form of a coating 24 on the bulb for absorbing all the visible radiations generated within the bulb while freely transmitting all, or at least a portion of, the invisible radiations. The said coating 24 consists of a of the base shell ll eliminates, or greatly minimizes, the stretching and thinning out of the lacquer coating 24 at the junction between the bulb and the base shell such as would normally 5 gpermit transmission to some degree of the visible radiations generated within the bulb. As shown in Fig. 4, the filler material 25 preferably overlaps or extends down onto the outer surface of the base shell M for a short distance, such as suitable material, such as a lacquer, which is capable of effectively absorbing all the visible radiations and freely transmitting all or part of the invisible radiations such as the infrared and/or ultraviolet rays. For infrared transmitting purposes, I have found the material commercially known as Eastman No. 20714 infrared transmitting lacquer, manufactured and sold by theEastman Kodak Company of Rochester, New York, to be particularly suitablia.

The coating 24 of light-absorbing lacquer is applied to the lamp ill by immersing the lamp, base up, in a bath of the lacquer material so that the entire exposed portion of the bulb ID, as well as the base shell H for a short distance from the mm 20 thereof, are submerged in the lacquer so as to form a coating over the entire exposed outer surface of the bulb and the rim portions of the base shell. The lamp is then removed from the bath of lacquer material and placed in a drying oven where the lamp is heated at a temperature of the order of 50 C. to dry the lacquer coating 24 on the bulb. The above coating operation may be repeated, if desired, so as to provide a double coating of the light-absorbing material on the bulb.

In accordance with the invention, I have found that, whatever their cause, the formation of light-transmitting bubbles and thin spots in the lacquer coating 24 at the junction of the base shell H and bulb ii! such as would normally allow transmission of visible radiations, is prevented by the application of an intermediate layer or fillet 25 of suitable filler material to the said junction between the bulb and base prior to the application of the light-absorbing coating 24 to the bulb. The said filler material 25 completely fills any annular space remaining between the bulb ill and the rim portions of the base shell I4 and, in addition, fills the "corner between the bulband the rim 20 (as shown in Fig. 4) so as to present a smooth continuous surface for the lacquer coating 24 to ride up as the lamp is immersed in the lacquer coating bath. As a result, there are no pockets or crevices at the junction between the base shell ll and the bulb l5 within which air could be trapped, during the immersion of the lamp in the lacquer coating bath, such as might cause the formation of light-transmitting bubbles in the lacquer coating 24 at the said junction. Moreover, the filling of the corner between the bulb ill and the rim 2!) of an inch or thereabouts. so as to assure the complete filling up of the corner between the bulb and the rim 20 of the base shell and produce a fillet the outer surface of which merges into the outer surfaces of the bulb II and base shell I4 so as to form one continuous and uninterrupted surface therewith.

The fillet 25 is made of a material, such as a natural or synthetic resin, shellac, lacquer, or other resinous material, which will readily fill up the space and the corner between the bulb II and the rim 20 of the base shell I and which is suiiiciently plastic so as not to crack on drying. A high-viscosity shellac composition, however, is preferably employed as the filler material 25. A suitable dark-colored material, such as a dark blue or black dye or pigment, is preferably added to the filler material 25 so as to render the filler material itself light-absorbing and thus further insure the complete absorption of all visible radiations at and adjacent the junction of the base shell with the bulb.

The filler material 25 may be applied to the lamp in any suitable manner, such as by painting it on with a small brush. Preferably, however, the filler material 25 is deposited on the lamp by a thin metal disc or roller which rotates through a pool of the shellac or lacquer filler material and with which the lamp is held in rolling contact, the lamp being held in a. freely rotatable holder and being pressed into engagement with the flat peripheral edge of the rotating disc in such a way that the said peripheral edge contacts the lamp at the junction between the base shell and the bulb.

Following the application of the filler material 25 to the lamp, it is allowed to dry thereon after which the light-absorbing coating 23 is applied to the lamp bulb in the manner set forth hereinbefore.

While I have described the invention as applied to a photoflash lamp, it is obvious that the invention is applicable in all cases where it is desired to render the bulb of a lamp or similar radiation-emitting device (of the type comprising a bulb having a base attached thereto and radiant energy-producing means within the bulb) selectively transparent to certain only of the radiations generated by said radiant energy-producing means through the use of a radiation-absorbing coating on the exposed surface of the bulb.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A radiation-emitting device comprising a bulb, radiant energy-producing means within said bulb, a base secured to said bulb and substantially abutting against the wall of said bulb, a quantity of filler material disposed at and adjacent to the junction between the base and bulb wall to form a fillet theremtween, and a coating of radiation-absorbing material on the exposed surface of said bulb and on said fillet, said coating being selectively transparent to certain only of the radiations generated within said bulb by said radiant energy-producing means.

2. A radiation-emitting device comprising a bulb, radiant energy-producing means within said bulb, a base secured to said bulb and substantially abutting against the wall of said bulb, a quantity of filler material disposed at and adjacent to the junction between the base and bulb wall'to form a fillet therebetween, and a coating of radiationabsorbing material on the exposed surface of said bulb and-on said fillet, said coating being impervious to the visible radiations, but permeable to at least certain of the invisible radiations, generated within said bulb by said radiant energyproducing means.

3. A radiation-emitting device comprising a bulb, radiant energy-producing mean within aid bulb, a base secured to said bulb and substantially abutting against the wall of said bulb, a quantity of filler material disposed at and adjacent to the junction between the base and bulb wall to form a fillet therebetween, and a coating of radiation-absorbing material on the exposed surface of said bulb and on said fillet, said coating being impervious to the visible radiations, but permeable to infrared radiations, generated within said bulb by said radiant energy-Producing means.

4. A flash lamp comprising a bulb, actinic lightproducing means within said bulb, a base secured to said bulb and substantially abutting against the wall of said bulb, a quantity of filler material disposed at and adjacent to the junction between the base and bulb wall to form a fillet therebetween, and a coating of radiation-absorbing material on the exposed surface of said bulb and on said fillet, said coating being selectively transparent to certain only of the radiations generated within said bulb by said light-producing means.

5. A flash lamp comprising a bulb, actinic light-producing means within said bulb, a base secured to said bulb and substantially abutting against the wall of said bulb, a quantity of filler material disposed at and adjacent to the junction between the base and bulb wall to form a fillet therebetween, and a coating of radiationabsorbing material on the exposed surfac of said bulb and on said fillet, said coating being impervious to the visible radiations, but permeable to at least certain of the invisible radiations, generated within said bulb by said light-producing means.

6. A flash lamp comprising a bulb, actinic lightproducing means within said bulb, a base secured to said bulb and substantially abutting against the wall of said bulb, a quantity of filler material the wall of said bulb, a quantity of resinous material disposed at and adjacent to the junction between the base and bulb wall to form a fillet therebetween the outer surface of which forms one continuous and uninterrupted surface with the outer surfaces of said base and bulb wall, and a coating of radiation-absorbing material on the exposed outer surface of said bulb and on said fillet, said coating being completely impervious to.

- the visible radiations, but permeable to infrared radiations, generated within said bulb by said light-producing means whereby said flash lamp emits solely infrared radiations when flashed.

8. A flash lamp comprising a bulb, actinic lightproducing means within said bulb, a base secured to said bulb and substantially abutting against the wall of said bulb, a quantity of filler material comprising a shellac composition containing a dark-colored light-absorbing agent disposed at and adjacent to the Junction between the base and bulb wall to form a fillet therebetween the outer surface of which forms one continuous and uninterrupted surface with the outer surfaces of said base and bulb wall, and a coating of radiation-absorbing material on the exposed outer surface of said bulb and on said fillet, said coating being completely impervious to .the visible radiations, but permeable to infrared radiations, generated within said bulb by said light-producing means whereby said flash lamp emits solely infrared radiations when flashed.

9. The method of rendering completely lighttight the bulb of an electric device having a base abutting against the wall of said bulb, which method consists in first applying a quantity of filler material to the junction between the base and bulb wall to form a fillet therebetween, immersing said device, base up, in a bath of lightabsorbing material to form a coating on the exposed surface of said bulb and on said fillet, and then drying said coating.

GEORGE H. MERIDITH. 

